Solid external walls are prone to damp penetration. They rely upon the integrity of the external finish for their weatherproofing. Even in good condition, water penetration may occur during severe weather conditions. They are less efficient at retaining heat leading to higher energy usage and costs.
Cavity walls replaced solid walls for a reason, which is to improve thermal efficiency and prevent any moisture (which enters through the outer brick leaf), from transferring across the cavity. This can happen when the brick gets saturated and can’t hold any more moisture.
Wind Driven Rain Penetration
The issue with retrofitted Cavity Wall Insulation (CWI) is that it is sometimes installed into unsuitable, exposed, buildings whose walls can get saturated.
One of the main causes of failed CWI in residential properties in recent years is the stampede to fill as many cavity walls as quickly as possible, with disregard for the suitability of the property. It has to be said that every CWI installation does not causes a problem (materials commonly used include mineral wool, polystyrene beads, or polyurethane foam).
This should not be fitted into a wall with a cavity less than 50mm; the wall should be clear of rubble; and should not be exposed to driving rain. It’s important that the cavity is checked before insulating it and that the works only proceed if the wall complies with the British Standard. Unfortunately, hardly any cavity walls meet this requirement. They often contain unfilled mortar joints, debris down the cavity, and wall ties covered in mortar droppings.
Debris and CWI in wall cavity
Areas prone to high wind content are prime candidates for penetrating damp. For example, an 80-km/h wind exerts 41.3 kPa of pressure on a wall’s surface. This is enough pressure to force moisture into cracks of any size. Mortar joints must not show evidence of more than hairline cracking and raked or recessed mortar joints should be avoided in very severe exposure areas.
CWI is not inherently waterproof and if the potential exists to transfer moisture across the cavity, then problems can occur. The resultant problem if the CWI gets wet is that you will potentially have a very serious wall-based damp problem caused by bridging of the cavity wall and physical damp proof course and of course no benefit whatsoever from the alleged improvement in insulation.
The Building Research Establishment states in their BRE Good Building Guide 44: part 2: “Insulating masonry cavity walls – principal risks and guidance” (available from www.brebookshop.com) states, “There can be an increased risk of rain penetration if a cavity is fully filled with insulation, i.e. moisture is able to transfer from the outer to the inner leaves resulting in areas of dampness on internal finishes. Rainwater, under certain driving rain conditions, can penetrate the outer leaf of masonry leading to wetting of the cavity insulation, a reduced thermal performance and damage to internal finishes.”
This leakage takes usually takes place place at vertical joints in between adjacent bricks given mortar shrinkage. The problem is not necessarily due to poor workmanship but is an inevitable aspect of such constructions. (This is also why there are Cavity Trays and weep holes over window and door openings. These divert any moisture outwards via the weep holes).
Where retro-fitted cavity wall insulation (CWI) is installed to a poor standard, it can lead interstitial condensation and damp issues (perhaps I may write more on this in another blog!). CWI can also slump which can create cold spots in the wall. These gaps are generally to be found at the top of the walls. This means that this area will have a lower surface temperature than the surrounding wall so it may very well be at dew point temperature and condensation may develop on these cold spots.
If there are doubts about the installation, a thermal imaging survey should be carried out to identify any 'cold spots'.
Poorly filled cavity wall
The role of the guarantee agency CIGA and their current approach to ‘CWI claims’ have been constantly discussed, even at government level. Read reviews of customers experience with CIGA on Trustpilot. Indeed, the Cavity Wall Insulation Victims Alliance (CIVALLI) continue to campaign against poor CWI installations and support those people affected.
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